The present invention relates to a leg-wheel type mobile robot having wheels at the tip of its leg and capable of moving on an irregular ground.
As a moving system of a robot, there are moving methods based on wheels and legs. In the moving method based on legs, walking is performed by controlling the attitude of the robot on the basis of a ZMP (Zero Moment Point) as standard. The ZMP is the center of reaction force at a grounding point, and is a point on the floor surface where the moment by the reaction force becomes zero. When the robot is made to walk, it is necessary to perform control of the walking in consideration of inertia force due to the movement of the robot itself, gravitational force applied to the robot, reaction force received from the floor, and the like. When a walking pattern is generated so as to make the ZMP settled within a convex support polygon of the foot sole of the robot, the robot can be made to walk without overturning.
As for the moving method based on wheels, there are known a moving method as represented by a motor vehicle, which has three grounding points or more and static stability, a method as used for a motorbike, which maintains lateral stability by using the angular momentum of a tire, and a method based on a wheeled inverted pendulum, for dynamically maintaining stability by feeding back an inclination angle and an angular velocity in an advancing direction of a movable body, as shown in JP-A-2005-288561.
The moving method based on wheels is characterized in that it is excellent in the moving efficiency and the moving speed, but has a large limitation on the environment, in which the robot can be moved, and low ground adaptability. Further, the moving method based on legs is inferior in the moving efficiency and the moving speed, but has high ground adaptability.
Thus, there is known a method, as described in JP-A-2005-288561, in which in order to utilize both the above advantages by the combination of wheels and legs, two-legged walking is realized by turning a wheel sideways and increasing the contact area of the sole, as needed. Similarly, there is known a method, as described in JP-A-2001-138272, in which in order to realize more dynamic and higher speed movement as compared with a normal walking operation, a leg-type mobile robot is made to perform roller-skating by being provided with roller-skating shoes.